Recognition memory judgments can be based either on recollection of qualitative information about a previous event or on assessments of stimulus familiarity. Cognitive studies show that these two memory retrieval processes are functionally distinct. However, very little is known about the cortical substrates of these two processes, and significant gaps remain in our understanding of their functional properties. The specific aims of the current proposal are as follows. (1) Determine if hippocampal and parahippocampal regions contribute to recollection and familiarity by contrasting the recognition memory deficits of amnesic patients with hippocampal (H) and hippocampal+parahippocampal (HP) lesions. Previous studies showed that patients with HP lesions exhibited deficits in both recollection and familiarity. In order to identify whether these regions contribute differentially to these two processes it is now essential that we contrast the memory deficits of H and HP patients. By examining the cortical substrates of recollection and familiarity these studies will serve to test competing theories of recognition memory and will evaluate the functional specificity of regions within the medial temporal lobe in humans. (2) Determine if familiarity-based recognition judgments are based on conceptual implicit memory, by contrasting the effects of two experimental variables (i.e., semantic encoding and dividing attention) and medial temporal lobe lesions (i.e., H and HP lesions) on familiarity and implicit memory. The results will show whether familiarity and conceptual implicit memory exhibit similar cortical regions, and thus will provide a test of current models of recognition memory and implicit memory. 3) Determine the forgetting functions of recollection and familiarity in healthy subjects and patients with hippocampal and parahippocampal damage in order to further characterize these processes and cortical regions, and to test models that assert that hippocampal and parahippocampal regions support long-term and intermediate-term memory respectively.